Do cold air intakes give you better gas mileage?

Discussion in 'The Garage' started by GoingUp, Apr 28, 2008.

  1. GoingUp

    GoingUp Lifer

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  2. Scouzer

    Scouzer Lifer

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    Yes, marginally.
     
  3. Uhtrinity

    Uhtrinity Platinum Member

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    I guess it would depend on the car. The Insights get optimal mpg with a 120 degree F intake.
     
  4. sjwaste

    sjwaste Diamond Member

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    No, just about every EFI car is metering air on its way in, including density, and adding fuel to maintain the A/R that the ECU wants to keep.

    The idea behind a cold air intake is that they'll bring in denser air, so you'll be able to burn more fuel per stroke, meaning more power at a given load, if I understand it correctly. I'm not sure if that helps or hurts fuel economy, but I think the mileage claims are based mostly from a "less restrictive" intake so that less energy is lost in creating intake vacuum (when the pistons go down on the intake stroke).

    Could be a combination of the two, but I'm pretty sure leaning out the mixture is not how they help fuel economy. That said, you're not going to see big MPG gains from a freer flowing intake. I wouldn't advise spending the money on one if you have a stock car, since the stock intake is probably not too restrictive at those air flow levels. If you're running 20PSI out of a T88, you might need a big purple cone filter.
     
  5. senseamp

    senseamp Lifer

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    Probably lower mileage. ECU should maintain constant fuel to air mixture, so colder air will result in more fuel being injected. One reason why my mileage drops during winter.
     
  6. GoingUp

    GoingUp Lifer

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    Well that and the winter gas mix they use with more ethanol.
     
  7. alkemyst

    alkemyst No Lifer

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    I didn't do a before and after on my intake, but since adding my header, cat and exhaust my mileage has seemed to improve.

    It's only been a couple tanks so far...I am continuing to watch it.
     
  8. PlasmaBomb

    PlasmaBomb Lifer

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    Sounds about right.
     
  9. Dman877

    Dman877 Platinum Member

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    Header and exhaust will improve efficiency by reducing back pressure and power loss during the exhaust stroke. A cold air intake, as others have said, allows the engine to burn more fuel due to the denser air, thus reducing fuel economy (though I doubt the difference is even noticeable)
     
  10. alpineranger

    alpineranger Senior member

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    Cold air intake, headers and exhaust will generally reduce fuel efficiency. This is because they don't affect frictional losses inside an engine, but they do increase pumping losses. Because they allow an engine to generate more power at the same conditions (engine rpm + throttle position), the throttle will be closed more than otherwise, increasing pumping losses.

    This runs counter to what many engine designers are trying to do these days to increase engine efficiency. You decrease the max power output of the engine, allowing for a larger throttle opening and reduce pumping losses. Any variable displacement technology (where cylinders are deactivated), and atkinson cycle operation (for example in the toyota prius or the honda civic's r18) work in this manner.
     
  11. mwmorph

    mwmorph Diamond Member

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    It depends on the exhaust. To put it simply, backpressure is a important measure of how much torque you're creating at low to mid rpms which is why all cars don't just have a 4" exhaust back from the cat.

    Now horsepower is a function of torque and yes, too much low can decrease power. A equal length header followed by 4 piping with no cat on a 4 cylinder car will probably make you lose hp and torque cross the board.

    If you want to create better mileage, you want more torque down low so you don't have to bring the engine as high up to get it moving and you can stay in higher gears longer.

    What you're seeing is instead the switch from winter blend fuel to summer fuels. During winter months, you probably get a 85/15% blend of ethanol and gasoline, which means you're only getting 94.75% of the total energy content hat you'd get from a gallon of 100% gasoline.


    As for the OP, intakes won't noticeably improve anything besides making the "whoosh" intake noise louder. Power will be affected minimally and mileage will not go anywhere in any measurable amount.
     
  12. JeffreyLebowski

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    The increase is because of your exhaust. Stock exhaust systems are fairly restrictive, by freeing up the exhaust (making it easier on the engine to expel the exhaust) you are putting less load on the engine thus making it more efficient.
     
  13. Apex

    Apex Diamond Member

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    Depends on how the ECU adjusts the A/F and timing.
     
  14. OS

    OS Lifer

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    it doesn't matter either way in my experience